1. Field of the Invention
The present invention relates to a speed change reproduction recording apparatus for a video cassette tape recorder (hereinafter called a "VCR") of a digital high definition television (hereinafter called an "HDTV") and a method thereof capable of achieving a better resolution of picture during a speed change reproduction operation by separating a normal reproduction data and a speed change reproduction data from a digital HDTV signal, storing the thusly separated speed change reproduction data into a plurality of frame buffers, and alternately recording the speed change reproduction data outputted from the frame buffers on a corresponding track.
2. Description of the Conventional Art
Generally, the method of the digital VCR is classified into a method of compressing, recording, and reproducing the analog signal transmitted thereto using a decoder, and a method of recording and reproducing the analog signal without compressing the signal.
The digital type HDTV such as a U.S. Grand Alliance type is characterized to adopting the later method. In this case, a certain interface circuit is necessary instead of a decoder, and there is no distortion, so that a desired resolution can be achieved. However, in case of the transport recording method, a picture resolution decrease takes place during a forward/backward reproduction mode, that is, during a speed change reproduction, which is one of major functions of VCR.
In order to resolve the above-mentioned problems, a certain method of recording a bit stream of an HDTV signal in a transparent method in a digital VCR, was necessary, since a data rate for recording the bit stream transmitted thereto, is smaller than the record rate which denotes that a data can be recorded on a tape, a method of executing a speed change by recording a speed change reproduction data on a tape region by as much as difference was introduced in the industry.
That is, this method is directed to extracting a speed change bit stream from an HDTV bit stream inputted therein, recording the thusly extracted stream on a speed change reproduction region, and implementing a desired speed change picture during a speed change reproduction mode. Therefore, a recording track includes a normal reproduction region (hereinafter called a "normal region"), which is characterized in directly recording a recording track as a bit stream and a speed change region (hereinafter called a "trick region") which is characterized in recording a speed change reproduction bit stream extracted.
In a general azimuth recording method, since the tape in a normal reproduction mode runs at the same speed as in a recording mode, the head, as shown in FIG. 1A, runs along a track of tape, and a trace of the head is formed along the track. However, the head in a speed change reproduction mode in which the running speed of the tape is different from the recording mode, as shown in FIG. 1B, runs across the tracks, and the trace crossing the tracks is executed.
Therefore, a partial data is extracted from each track of the same azimuth in a speed change reproduction mode for a reproduction. In addition, since an HDTV bit stream is a compressed data type, only an intraframe coding bit stream can be decoded independently. Therefore, the data reproduced in a speed change reproduction mode in a VCR, in which an HDTV bit stream is recorded in order, includes a burst characteristic. That is, only a partial part of each track is reproduced. The speed change picture includes a bit stream of the intraframe. Therefore, a reproducing speed change picture has a disadvantage in that a partial picture is reproduced in a mosaic format.
Referring to FIG. 2, a conventional speed change reproduction recording apparatus for a VCR of a digital HDTV includes a syncblock unit 1 for receiving an HDTV bit stream having a video data and an audio data and for converting the thusly received data into a syncblock format which is a basic unit of a VCR record and reproduction, a buffer 2 for temporarily storing the syncblock outputted from the syncblock unit 1, a transport decoder 3 for decoding the HDTV bit stream and for separating a video bit stream from the HDTV bit stream, a video header decoder 4 for separating a bit stream coded for an intraframe from the video bit stream outputted from the transport decoder 3, a variable length decoder 5 for executing a variable length decoding operation so as to recognize a codeword contained in the bit stream separated by the video header decoder 5, a speed change data extractor 6 for separating a direct current voltage component and a low frequency component from a codeword outputted from the video header decoder 5, a transport encoder 7 for packeting a speed change reproduction video bit stream outputted from the speed change data extractor 6 to have the same format as the normal reproduction bit stream, a syncblock unit 8 for converting the bit stream outputted from the transport encoder 7 into a syncblock format, a buffer for temporarily storing the syncblock outputted from the syncblock unit 8, a track record format unit 10 for providing a record timing corresponding to each record format, and a multiplexer 11 for outputting a normal bit stream of the buffer 2 or a speed change reproduction bit stream of the buffer 9 to an error correction coding unit (not shown) in accordance with a record timing outputted from the track record format unit 10.
The operation of a conventional digital VCR recording apparatus will now be explained with reference to accompanying drawings.
To begin with, as shown in FIG. 3, the HDTV bit stream is transmitted to the syncblock unit 1, and the HDTV bit stream is converted into a syncblock format which is a basic unit of a VCR record and reproduction. Thereafter, the HDTV bit stream is stored in the buffer 2 and multiplexed by the multiplexer 11 with a speed change reproduction stream. In addition, the HDTV bit stream becomes a speed change bit stream through a transport encoder 3, a video header decoder 4, a variable length decoder 5, a speed change data extractor 6, a transport encoder 7, a syncblock unit 8, and the buffer 9, in order.
That is, in order to extract the speed change reproduction data, the transport decoder 3 separates a video bit stream by decoding the transport packet of the HDTV bit stream containing a video bit stream, an audio bit stream, and an extra data bit stream and outputs the thusly separated video bit stream to the video header decoder 4. The video header decoder 4 separates a decoding intraframe bit stream from the video bit stream and outputs to the variable length decoder 5.
Since the HDTV bit stream is variable-length-decoded so as to obtain a desired high compression rate, the variable length decoding is executed so that each codeword of bit streams can be recognized. Thereafter, the speed change data extractor 6 separates a direct current voltage and a low frequency component from the codeword contained in the intraframe. That is, since the tape region corresponding to the speed change reproduction region is limited to its size, it is necessary to extract a bigger component which plays a more important role in achieving a desired speed change picture; however, the resolution of the speed change picture decreases compared with the normal reproduction.
The transport encoder 7 changes the speed change reproduction video bit stream to a bit stream corresponding to a syntax of the HDTV bit stream, and changes to a normal reproduction bit stream by transport-packeting it, and the syncblock 8 changes the bit stream to the syncblock and outputs to the buffer 9.
The thusly obtained normal reproduction bit stream and the speed change reproduction bit stream are multiplexed by the multiplexer 11 in accordance with a record timing signal outputted from the track record format unit 10 and outputted to the error correction coding unit (not shown). Here, the record timing signal is a kind of a control signal corresponding to a record format of a normal reproduction bit stream and a speed change reproduction bit stream each recorded on the normal region and the trick region of the tape.
In case that a data is. recorded on the normal region or the trick region, the surface of the trick region is determined by a record rate of the VCR, and the position of the trick region on the track is determined by a speed change algorithm. These surface and position of the trick region are directly related to the quality of the speed change reproduction and affects a two-speed reproduction function and a head tracking unit.
The method of setting the above-mentioned trick region is classified into a trick play track method of separating a trick region along a head reproduction trace in accordance to a certain speed as shown in FIG. 4A and a method of doubly recording the same bit stream by a track unit by separating a beginning part, an intermediate part, and an ending part in each track irrespective of the certain speed.
Two or three speed change reproduction methods can be available in the conventional digital VCR, and FIGS. 4A and 4B show three speed, nine speed and twenty seven speed, respectively.
However, in the conventional speed change method, when recording the speed change data on a track, it is possible to achieve a desired speed change picture by tracking a certain position, and it disadvantageously requires a certain tracking algorithm such as a servo-control.
In addition, in case of the method of separating a trick region along a trace of the head in accordance with a certain speed, since a speed change reproduction data corresponding to each speed is positioned in accordance with a head-limited tracking start position, an additional tracking algorithm for a speed change is disadvantageously necessary since a certain speed data is reproduced after the head is positioned at the starting position corresponding to a certain speed. Moreover, since a certain recording position is given in accordance with a certain speed, a more complicated formatting algorithm and memory configurations are necessary.
In order to remove the conditions that a tracking start position should be positioned at a specific position, in case that decreasing the bit number per picture, allocating the start portion, the intermediate portion, and the end portion of each track irrespective of the speed type without considering the frame rate of the certain speed picture so as to double-recording the bit stream by one track unit in case of the previously defined maximum speed, it is necessary to record the data amount reproducible from a track in every track during a certain period. In addition, even though it is possible to obtain a speed change picture at a predetermined position, the better resolution cannot be achieved because the speed change reproduction data is ineffectively double-recorded on the allocated speed change region because the speed change reproduction data and because a certain resolution determined by the maximum speed type is continuously adopted at a low speed.